The present invention relates generally to the instrumentation field, and more particularly, to systems for monitoring the rotational velocity of a shaft.
There are sytems known in the art for both sensing the current rotational speed of a shaft and also for monitoring shaft speed. However, such systems are narrowly configured in general to monitor shaft speeds in preset unadjustable ranges. As a result, custom circuits must be adapted to the various user requirements. In addition, the known monitoring systems may typically be configured with an alarm device which is activated as soon as a detected speed change occurs. As a result, such systems may readily be subject to false triggering resulting from noise. Such systems also are not capable of operating in an overspeed detection mode under conditions where relatively short excursions of shaft velocity beyond the predetermined limits are permitted, or in an underspeed detection mode under conditions where the shaft velocity must continually remain above the limit for at least a predetermined period in order to avoid an alarm condition.
Furthermore, the prior art systems typically include sensors which are indirectly coupled to the shaft to be measured, for example, through the use of belt or chain drive mechanisms. With such mechanisms, these systems are relatively large, have relatively large maintenance requirements, and are subject to the failure of the belt or chain drive mechanisms. Although certain prior art systems employ optical sensors which are coupled to a shaft to be monitored, those systems often either are inaccurate due to ambient light-induced noise, or include relatively complex and correspondingly expensive light tight housings for the sensor assembly.
Accordingly, it is an object of the present invention to provide a monitoring system having an adjustable controlled limit about which shaft rotational velocity is monitored.
It is another object of the present invention to provide a shaft rotational velocity monitoring system in conjunction with an overspeed alarm device, whereby relatively short excursions in shaft velocity above a preset limit are permitted without initiating an alarm condition.
Still another object of the present invention is to provide a shaft rotational velocity monitoring system in conjunction with an underspeed alarm device, whereby the shaft must maintain a velocity above a preset limit for at least a predetermined interval in order to avoid an alarm condition.
Yet another object of the present invention is to provide a direct coupled shaft rotation sensor in conjunction with a means to monitor the shaft rotational velocity.
A further object of the present invention is to provide a direct coupling sensor to a shaft to be monitored in order to permit a relatively small, and low maintenance shaft velocity monitor.
Another object of the present invention is to provide a monitoring system having a shaft rotational velocity detector and associated monitor and alarm circuit which may be adapted to identify times a which a shaft is rotating above a predetermined speed or to identify times at which a shaft is rotating below a predetermined speed.
It is a further object of the present invention to provide an optically coupled sensor for a shaft rotational velocity monitor wherein the sensor is operative in the infra-red portion of the spectrum, thereby providing relatively high immunity from error caused by ambient light.